Present state of the art for odometer aided inertial systems models a vehicle suspension system as a rigid body. Odometer aided inertial systems create an integrated navigation solution. The integrated navigation solution contains data such as vehicle position, vehicle velocity and vehicle attitude. In addition to these primary system outputs, the odometer aided inertial system calibrates the odometer with an odometer error model. Because the inertial system is mounted on the vehicle body and the odometer measures motion of the chassis, the odometer aided inertial system attempts to estimate the orientation between the vehicle body and the vehicle chassis. The body of this vehicle is defined as the upper part of this vehicle containing the engine, occupants, ammunition, etc. The vehicle body rests upon the vehicle chassis which is defined as the under part of this vehicle consisting of the frame with axles and the wheels or tracks.
This inertial/odometer error model works well when the integrated solution can estimate the relative orientation of the vehicle body to the vehicle chassis with a 0.08 degree or better accuracy. The assumption of constant relative orientation does not work well when the vehicle body moves significantly relative to the vehicle chassis. In some vehicles, this motion can be as much as two degrees. Significant errors in the odometer calibration occur when changes in this orientation are not modeled correctly. These errors in odometer calibration degrade the primary system outputs. Both vertical velocity and vertical position (altitude) are degraded because of the odometer modeling errors. Therefore, it would be beneficial to have the primary system outputs be optimally accurate. Further, it would be beneficial if the odometer modeling errors could be minimized or eliminated.